1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device of which an output characteristic is variable according to a code fed thereto.
2. Description of the Prior Art
With the diversification of electronic products and needs for them, production of electronic products is shifting from conventional small-variety large-quantity production to large-variety small-quantity production. To cope with this trend in increasing market competition, suppliers of semiconductor integrated circuit devices are required to supply product manufacturers or the like with a large variety of semiconductor integrated circuit devices with short delivery times.
For suppliers, however, developing and fabricating such semiconductor integrated circuit devices is inefficient, contributing greatly to increased costs. For this reason, to cope with the aforementioned trend, suppliers of semiconductor integrated circuit devices in the field of logic circuits, in particular ASICs including gate arrays, are supplying their users such as product manufacturers with field-programmable gate arrays and programmable logic devices (PLDs) that permit the users to modify the configuration of the circuits incorporated therein within certain limits when they manufacture products.
As described above, such programmable semiconductor integrated circuit devices are composed of logic circuits, and are used with their logic configuration appropriately modified. Thus, with these devices, it is difficult to vary a characteristic of an analog output, such as the amplification factor or the output voltage. To overcome this, Japanese Patent Application Laid-Open No. H9-330135 proposes an operation characteristic correction device in which an analog output is kept constant according to the value of a control register. With this device, however, even if a wrong value is set, it is difficult to recognize it, and it is impossible to supply the device as semiconductor integrated circuit devices of a single type but with different specifications to a plurality of users.
An object of the present invention is to provide a semiconductor integrated circuit device that, with a single type of it, can yield an output with different characteristics desired by different users simply by being fed with one of codes assigned to different characteristics and that is provided with an output terminal that permits the checking of whether the correct code has been entered or not.
To achieve the above object, according to one aspect of the present invention, a semiconductor integrated circuit device is provided with a control circuit that decodes and outputs a predetermined portion of an input code as a driving signal; a switching circuit composed of a switching device that is driven by the driving signal; and an analog circuit in which connection of an internal device is varied according to the state of the switching device so that the analog circuit outputs an output signal with an electrical characteristic according to the input code.
The input code may consist of a characteristic setting code that corresponds to the predetermined portion of the input code and that determines the electrical characteristic and a user code that is assigned uniquely to each user of the semiconductor integrated circuit device.
The switching device may be a MOS transistor.
A registration code corresponding to the user code may be set previously in the semiconductor integrated circuit device. In this case, the semiconductor integrated circuit device is further provided with an error output terminal by way of which a signal indicating an abnormality is output when the user code entered does not agree with the registration code.
According to another aspect of the present invention, a semiconductor integrated circuit device is provided with: a control circuit that decodes and outputs a predetermined portion of an input code as a driving signal; a switching circuit comprising a plurality of switching devices that are driven by the driving signal; a power supply circuit in which connection of an internal device is varied according to the states of the switching devices so that the power supply circuit outputs an output voltage selected uniquely from among a plurality of voltages according to the input code; and an internal analog circuit that can use as a reference voltage one of the plurality of voltages output from the power supply circuit and of which an output characteristic is varied according to the uniquely selected output voltage.
The input code may consist of a characteristic setting code that corresponds to the predetermined portion of the input code and that determines the electrical characteristic and a user code that is assigned uniquely to each user of the semiconductor integrated circuit device.
The power supply circuit may control the output voltage thereof by feeding a predetermined voltage to one input terminal of an amplifier, dividing the voltage on the output side of the amplifier with a plurality of resistors, and feeding the resulting divided voltage negatively back to the other input terminal of the amplifier.
A registration code corresponding to the user code may be set previously in the semiconductor integrated circuit device. In this case, the semiconductor integrated circuit device is further provided with an error output terminal by way of which a signal indicating an abnormality is output when the user code entered does not agree with the registration code.
The plurality of resistors, except the one always connected to the output side of the amplifier and the one always connected to ground, may correspond one to one to the plurality of switching devices. In this case, as one of the switching devices is driven, the ground-side terminal of the resistor corresponding to that one of the switching devices is connected to ground.
The switching devices may be MOS transistors.